Drop plug



R. N. MILLER DROP PLUG original Filed March' 1, 1941 Patented Mar. 9, 1943 DROP PLUG Robert N. Miller, Rosemont, Pa., assigner to The Pennsylvania Railroad Company, Philadelphia, Pa., a corporation of Pennsylvania riginal application March 1, 1941, Serial No. 381,272. Divided and this application October 12, 1942, Serial No. 461,693

2 Claims.

This invention relates to safety plugs for steam boilers of the type comprising a hollow body component with a drop member normally sustained therein by a fusible bushing Iadapted to melt and release said member, under high temperature, for giving notice that the water in the boiler has lowered to an undesirable level. Drop members of the noted species are held in the body'components by press-fitting or other assembly means, while relative creeping is normally prevented by axial compression of the fusible bushing.

The present application is a division from a prior one 'filed by the present applicant and William B. Miller under Serial No. 381,272, March l, 1941, and allowed ,April 16, 1942; Patent No. 2,301,633.

The primary object of this invention is to provide a safety plug of the indicated type embodying refinements whereby the drop member is initially secured .concentric with the axis of the body Vcomponent bore and so retained until the intervening fusible bushing has suiciently melted to permit the steam pressure in the boiler to blow said drop member directly out without any axial misalignment or tilting tendency conductive to sticking or leakage (passage) of steam into the fire-box, until the drop member is ejected.

Another object is the provision of an improved cold assembled safety plug in which the releasable member is .positively retained in place against creeping until the moment when it is to be blown out.

Subsidiary objects, with ancillary advantages, will be understood as the nature of the invention is more fully disclosed, said invention consisting essentially in providing the safety plug body component With a converging bore having annular recesses at the outer and inner ends thereof and, incidentally to force tment therein of a drop member with end surrounding recesses for confronting registration with the body component annular recesses, laterally expanding the intervening fusible sleeve ends into the said recesses of both members.

The accompanying sheet of illustrative drawing exemplifies a preferred embodiment of this invention, and wherein similar reference :characters are applied to corresponding parts in all the views; while the concluding claims more particularly recite the -features of novelty over the prior art.

In the drawing:

Fig. 1 is a vertical section through the body component (or member) included in the illustrated typical embodiment of this invention.

Fig. 2 is a similar section including the fusible sleeve and drop plug, in initial assembly, and with fragmentary Iportions of appropriate securing means indicated by dot-and-dash lines.

Fig. 3 is a corresponding section illustrating the finished plug installed in a boiler crown sheet; and,

Fig. 4 is a perspective view of the drop plug.

In the following detailed explanation of this invention, specific terms will be employed for the sake of clarity, but it is to be understood such terms are used in a descriptive sense onlyV and not for purposes of limitation, each said'term being intended to include all technical equivalents which serve in a similar capacity to accomplish an analogous end.

Referring to the embodiment of this invention shown by Figs. 1-4 inclusive, the body component of the improved safety of drop plug is comprehensively designated by the numeral I, said component embodying a machined cylindrical portion 2 having an inwardly converging bore 3, and an externally taper threaded part 4 for screw engagement in a correspondingly threaded aperture `5 provided for its reception in the boiler crown sheet I5.Y

The bore 3 is, preferably, formed with an inward taper of substantially three-quarters Aof an inch to the foot; while the bore of the taperthreaded part 4 includes an inner cylindrical counterbore 9, and an outer rectangular socket section I0, with the diagonally opposing corners angularly lleted at II, as in the prior application hereinbefore identified.

Adapted for snug engagement in the plug bore 3 is a complementally tapered fusible material bushing I2 of even surrounding thickness and smooth circumferential nish, interiorly and exteriorly. This bushing I2, as shown to best advantage in Fig. 2, is of a longitudinal dimension substantially approximating that of the bore 3, and it preferably consists of an alloy containing eighty-five per cent lead with fifteen per cent tin; although any other suitable fusible alloy or mixture can be used.

The solid releasable closure member I 3 is preferably of brass and a longitudinal taper complemental to that of the Ifusible bushing bore I4, but it is of fractionally greater diameter so that, when said member is initially inserted in said bore I4,

it approximately occupies the position shown in Fig. 2, for a purpose later explained.

The bore 3 of the annular portion 2', it is to be particularly noted, is of a substantially plain taper with a concentric annular recess 20 at the larger end and a similar spacially related one 2I at the lower end, whereby the intervening portion of the bore surface forms an inner continuous annular projection 22; while the releasable member or drop plug I3 is provided` with end, or upper and'rlower reductions deiining sur-- rounding recesses 23, 24, respectively, for con- Y,

fronting registration with the body annular re4 cesses 20, 2|.

In assembling the plug I as described, it will be readily understood that the body portion- I is placed over a suitable stationary die I'I, Fig. 2, freely tting the counter-bore 3 and spaced from the bottom of the bore of the portion 2, when the fusible bushing I2 is inserted in the boreS with its smaller end also seating on said die.,l

The releasable solid member I3 is next deposited in the bore I4 of the bushing I2, whereupon a movable die I8, Fig. 2, is moved into engagement` withthev upper end I9 of the releasable member Due to such press-fitting of the parts I, I2 and.

I3 together, it will be obvious,l said parts are firmly interlocked; while no burr will be formed either at the top or bottom of the. bore 3,

or around the corresponding ends of the releas-4 able plug I3.

Still further, it will be quite obvious that when low water in the boiler over the crown sheet 6 takes place, with resultant exposure of the top end I9 of the drop plug I3, the fusible bushing I2 will' rapidly become overheated and melt, whereupon said plug will' be blown out by the steam pressure, into the fire-box. Finally, due tothe vertically spaced flange-like interengagement of the fusible sleeve I2 with the body portion 2 and ends 23, 24 of the drop plug I3, said plug is normally retained coaxially within the bore S-until approaching the blow-out point, irrespective of any downward movement due to softeningI and progressive melting of the fusible sleevey I2', prion to its forced ejection into the rer-box.

Having thus described my invention, I claim:

1. In a drop plug, a body component including a cylindrical portion having an` inwardlyv converging bore intermediate spaced, annular; re;.. cesses; a releasable closure, member having endv reductions defining surrounding recesses for. con.-. fronting disposition Vrelative to the annular re,- cesses in the cylindrical portion` bore; and. a. fusible material plain bushingY intermediate the. cy-` lindrical portion bore andv the closure member' with its ends laterally expanded intoy the inter--v vals jointlydefined by the, annular recesses. in the body and closure.

2. The combination of claim l wherein. the

body component annular recesses, and the closure,

member surrounding. recesses, are ofrectangular cross-section and concentrically-related.

ROBERT N. MILLER'. 

